1. Field of the Invention
The invention relates to a method for charging a battery and, more particularly, to a technique for charging a battery at a high temperature.
2. Description of the Related Art
A typical battery charger includes three control circuits, a constant current control circuit, a constant voltage control circuit, and a constant temperature control circuit. When a battery with less electric quantity is charged, the battery charger enters a constant current mode. At that moment, the constant current control circuit may keep a stable charging current to charge the battery. Generally, the temperature of a conventional charger is between 0 degree centigrade (° C.) and 45° C., and the conventional charger may charge the battery continuously in the constant current mode as long as the voltage of the battery is less than 4.2 volts (V). When the voltage of the battery reaches 4.2 V, the charger switches to a constant voltage mode. At that moment, the current becomes less and less gradually until the battery is fully charged.
When the voltage of the battery reaches a preset voltage which is usually 4.2V, the conventional charger enters the constant voltage mode. At that moment, the constant voltage control circuit in the conventional charger may charge the battery with a constant voltage. When the constant temperature control circuit detects that the temperature of the battery is higher than 45° C., to avoid the expansion and liquid leakage caused by charging the battery at 4.2V voltage and high temperature, even the voltage of the battery does not reach 4.2V, the conventional charger stops charging the battery immediately when the preset temperature such as 45° C. is reached. However, a battery cell may be charged with a small constant voltage such as 4.1V at the temperature between 45° C. and 60° C. The conventional charger cannot switch the charging voltage according to the temperature change. Therefore, when the temperature is between 45° C. and 60° C., even if the voltage is low, the battery cannot be charged. Therefore, conventionally, when the temperature is higher than 45° C., the battery cannot be charged, and the battery is charged when the temperature is lower than 45° C.